For the demands of speeding-up, miniaturization, and the like in the recent years, a toner that is capable of being fixed at an even lower temperature is in demand. In order to meet such a demand, a toner in which a resin binder containing a crystalline resin and an amorphous resin is used is proposed. While a toner in which a crystalline resin and an amorphous resin are used as described above has improved low-temperature fixing ability, the toner described above is likely to have a lowered resin strength. As a result, various disadvantages are more likely to take place, such as a disadvantage concerning the lowering of durability caused by deposition on a developer blade or generation of filming on a photoconductor when a toner is applied with a larger mechanical or thermal stress due to the speeding-up and miniaturization, and a disadvantage in fall-off of toner, which is a phenomenon in which toners are dropped off from a developer roller. These disadvantages are especially serious when a toner is applied to a nonmagnetic monocomponent developer device in which toners are charged by frictional forces with a developer blade, or when a toner is applied to an oil-less nonmagnetic monocomponent developer device in which a releasing agent must be contained in the toner in a large amount.
In view of these disadvantages, a method for producing a toner including the steps of melt-kneading a crystalline polyester and an amorphous resin, and heat-treating a melt-kneaded mixture to obtain a toner which satisfies all of low-temperature fixing ability, storage property, and durability is proposed (see JP-A-2005-308995 (US-A-2007/207401) and JP-A-2009-116175 (US-A-2009/123863)).
In addition, a toner containing a resin binder containing a block copolymer or a graft copolymer obtained by chemically bonding 3 to 50 parts by weight of a crystalline polyester and 97 to 50 parts by weight of an ionically cross-linked amorphous vinyl polymer, wherein a chloroform-insoluble content is from 3 to 10% by weight of the copolymer is shown to have excellent offset resistance and low-temperature fixing ability (see JP-A-Hei-4-81770).
As a method of improving fall-off of a toner, a method including the step of adding fine magnesium silicate compound particles surface-treated with a fatty acid to a toner as an external additive is proposed (see JP-A-2007-240716 (US-A-2007/190443)).